This study shows that microcrystal tests can act as presumptive tests when color-based tests are not feasible. GHB and GHV were identified in some complex matrixes and clearly differentiated between the two based on crystal characteristics. When the atomic arrangement of a crystal can be positively determined and associated with a specific drug, the microcrystal test is no longer presumptive; it becomes conclusive. The key is the analyst's ability to recognize the crystal and apply quantitative measures, such as size and angles, to verify interpretation. Distinct microcrystals formed with silver (+1) and lanthanum (+3) ions, but not with the copper (+2) ions. The crystals formed with GHB were distinctly different from those formed with GHV, and in all cases the dry microcrystals were readily distinguished from reagent crystals. X-ray diffraction analysis provided definitive structure for the microcrystals. The method can be applied to the detection of GHB and GHV in many types of beverages; however, for wine, beer, and some mixed drinks, some type of additional sample extraction and preparation will be required before the method can be generally applied to casework. To perform the crystal test, one drop of sample solution that contained the analyte of interest was placed on a glass microscope slide, followed by a drop of crystallizing reagent. For initial work, water solutions of the two analytes were also examined. The resulting solutions of analyte and reagent on the slide were dried at room temperature and examined with a LeicaDMLP polarizing microscope at a total magnification of x100. Individual crystals were isolated with micromanipulation techniques, and diffraction data were obtained. 2 tables, 1 figure, and 20 references